The color ranges from black to red, yellow, green, grey, blue,
purple, etc. Most of the slate is used for decoration or "culture
stone" as the local customers call them. Here are
some of the general picture of the areas.

Slate from Men Tou Gou has been used for roofing for over 500
years. Most of the present production, about 80%, is exported
for flooring, walls, roofing etc. The color varies: black,
black grey, purple, green, jade green etc.

The green slate from Fang Shan is very popular. It is used
for billiards table.

2. Shaanxi:

The slate vein runs for over 200 km eastwest with 50 km wide.
The most of the slate was formed in the age from Ordovician
to Cambrian periods. In this area, they have the beautiful,
high quality black slate and 50% of national production
capacity. People from Germany, France, Belgium, UK, Spain,
as well as US have come to visit the area for sourcing,
purchasing, investment etc.

3. Hubei:

Zhu Xi and Zhu Shan area is supposed to have the largest reserve
of slate from Cambrian, Ordovician and Silurian periods.
The color includes black, grey, bean green and green. But
the overburden is large with average about 50 meters.

Although slate has been used for 500 years in China, yet as
an industry it started about 20 years ago. The story goes
like this: in early eighties when China initiated its open-door
policy, one former Minister from Urban Construction Ministry
saw the expensive "stone" being used on top of
roofs when he was visiting the States. So when he came
back, he assigned his associates to find the same stone
to export. One of the first places identified is Ziyang
in Shaanxi province.

However, it was not until the middle of nineties of last century
that China started to realize that some slate was fading
and some was not, and also there are other issues like
water absorption and acid resistance for slate. I think
that is the reason you found both good slate and poor quality
slate in the same crates. With the introduction of new
processing machines from Europe, as well as the quality
control concept, China was able to produce good quality
slate though with disappointing quantity.